1. Field of Art
This invention relates to inspection means and in particular to a method and apparatus for determining whether light or other radiation will pass through an article such as a can end which is inspected for small openings.
2. Description of the Prior Art
It is well known to inspect for holes in articles by shining a light on one side of the article and inspecting the opposite side for light emanating from openings in the article using photosensitive means such as a photoelectric cell or the like. Systems of that type are disclosed in a number of U.S. Pat. Nos. such as Linderman et al 3,416,659; Phillips 3,453,054; Dvacho et al 3,750,877 and Trimble et al 3,826,923 among others.
In employing light to inspect articles, the light sensitive or photosensitive means must usually be shielded against ambient light and against light from the source passing around the article which is being inspected. A common way of shielding the photosensitive means is to put it in a light tight enclosure having an aperture or apertures therein in which the articles to be inspected are positioned during inspection. The use of such a light tight enclosure can slow the inspection process and can present problems in locating the photosensitive means in close quarters such as adjacent a press on which the articles are being formed. The photosensitive means is also usually relatively sensitive to vibrations and impact which could damage such means. It is therefore desirable for the photosensitive means to be disposed in a fixed position and insulated from shock.
An improved method and apparatus are desired for rapidly inspecting opaque articles for openings therethrough.